Usually, in a plug body for plugging an opening in a gas tank, plural passages for communicating between the inside and outside of the gas tank are formed, and plural valve devices are also assembled such as a manual valve for shutting off the flow of high pressure gas within the passages or a check valve for preventing adverse flow of the gas (see, for example, Japanese Patent Laid-open Publication No. 09-210296).
In recent years, a gas tank for hydrogen mounted on a fuel cell vehicle or the like have tended to be designed so that hydrogen can be stored at higher pressure to increase the amount of stored hydrogen. Moreover, the number of valves assembled to the plug body for the gas tank has also tended to increase to achieve higher reliability for higher pressure of the stored hydrogen, or for high precision capability in regulating the pressure. For example, although the manual valve or check valve provided in a filling passage through which hydrogen passes for filling the gas tank, an additional check valve is preferably introduced to provide multiple valves for system redundancy to achieve reliability for the stored hydrogen at higher pressure. However, the increase in the number of valve devices assembled to the plug body makes the plug body larger, and assembly of the valve device complicated.